The present invention relates to a process for manufacturing cured opaque coatings with a high hiding power based on paste filler compositions of radiation curable unsaturated polyesters and copolymerizable monomers. The invention further relates to these paste filler compositions for producing the cured, opaque coatings with high hiding power. Such coatings serve as dense and continuous, opaque layers with excellent hiding power on various substrates. They also serve as filling material for cavities to make subsequent lacquering possible.
It is known to use highly filled, pigmented polyester paste filler compositions as coating agents for different substrates. They are applied, for example, to substrates of wood, materials based on wood, plastics, metals and the like. These known polyester paste filler compositions contain unsaturated polyesters and copolymerizable monomers as film-forming binders. Curing is effected by copolymerization of the components using suitable curing agent systems, such as peroxide curing agents and metal or amine accelerators. These materials are two-component materials which are difficult to handle. The time required for curing and for manufacturing of cured layers is considerable. The hiding pigments present in these prior art polyester paste filler compositions prevent a transparency necessary for the penetration of rays and as a result curing by means of UV radiation or sunlight is not possible.
Transparent and clear unsaturated polyester compositions can be cured with UV rays if a special UV sensitizer is present. As a result clear coatings are obtained and can be used as clear lacquers in the lacquering of wood, the wood grain remaining visible.
According to German Published Application DAS No. 1,621,820, radiation curing by the use of UV rays can still be performed if the transparent polyester paste filler compositions contain filler material of very low hiding power. The resulting coatings do not have sufficient hiding power. Curing of unsaturated polyesters and copolymerizable monomers with UV rays permits an economical and simple manufacturing of lacquered materials, due to the very short curing times. For the reason, however, that only transparent and clear coatings could hitherto be cured, the application of UV curing has been very limited.
The present invention relates to a process for manufacturing cured opaque covering layers with high hiding power from polyester paste filler compositions by radiation curing. This process increases the range of application of radiation curing.
The term "polyester filler compositions" in the subsequent text, includes all preparations based on liquid paste filler or coating compositions, used as coating agents for the manufacture of coating layers on wood, wood materials, plastics, hardboard, molded plastic materials, metals, brickwork, concrete, cement, quite generally on any desired substrate. The term also includes the compositions disclosed in assignee's copending application Ser. No. 337,063, now U.S. Pat. No. 3,933,875 entitled "Opaque Molded Polyester Copolymer Articles and Coatings".
In these cases the coating covers the substrate completely or partially. It can be employed for filling cavities, for priming and for the production of smooth coatings for subsequent lacquering. In addition, the polyester paste filler compositions can be applied onto the existing lacquer coatings.
The polyester paste filler compositions consist of radiation curable unsaturated polyesters and copolymerizable monomers. Unsaturated polyesters are described in detail and summarized, in the standard literature "Polyesters and Their Applications" (Bjorksten, Tovey, Harker and Henning. N.Y. Reinhold Publishing Corporation, 1956), "Polyester Resins" (Lawrence, N.Y. Reinhold Publishing Corporation 1960), and "Unsaturated Polyesters: Structure and Properties" (Boenig, Amsterdam, Elsevier Publishing Company, 1964).
The term "radiation-curable" in the subsequent text, includes those polyester paste filler compositions which can be cured by the use of irradiating UV rays, sunlight or more efficient ionizing rays. The term "radiation curing" includes all curing of coatings based on radiation curable polyester paste filler compositions by the use of UV rays, sunlight or more efficient ionizing rays. The known processes for radiation curing are summarized, for example, in the publications "Die Lichthartung von Polyester-Lacken" ("Curing Polyester Lacquers by means of Light") (Eugen Richter, "Moderne Holzverarbeitung", issue 10, 1968, pages 604-606) and "Lackhartung durch ultraviolettes Licht" ("Lacquer Curing by Ultraviolet Light") (Dr. Wolfgang Deninger and Dr. Manfred Patheiger, Industrie-Lackier-Betrieb, 37th year, issue 3, March 1969, pages 85-91).